1. Field of the Invention
The present invention relates to a sheet feed apparatus in an electrophotographic apparatus, and more particular to a sheet feed apparatus that uses airflow.
2. Description of the Related Art
FIG. 1 shows a configuration of a sheet feed apparatus that uses airflow in the existing electrophotographic apparatus, i.e., an apparatus which is generally called an airflow type sheet feed apparatus or an air pick sheet feed apparatus. In FIG. 1, sheets 2 loaded on a sheet lifting table 1 are controlled in such a way as to be constantly positioned at a fixed height, by a sheet upper surface detection sensor 3 and a controller 4. The controller 4 controls the driving of the sheet lifting table 1 based on information from the sheet upper surface detection sensor 3. A suction chamber 5, a belt member, which is generally called a suction belt 6, a plurality of holes through which air passes, and a driving device 7 for driving the suction belt 6 are located above the sheets 2. A nozzle 8 that causes an upper layer portion of the loaded sheets 2 to hover by air blowing is provided at a front of the sheets 2 in a conveyance direction. A sheet feeding is carried out as the suction belt 6 suctions and conveys the sheets 2 caused to hover by the nozzle 8. Also, a conveyance roller 21, a sheet conveyor, that receives the suctioned sheets 2 and conveys them to a not-shown image forming section, is provided downstream of the nozzle 8 in the sheet conveyance direction. In such a sheet feed apparatus, various devices have heretofore been made to obtain a sufficient sheet separation effect by the air blowing, i.e., to prevent multifeeding of sheet.
For example, as shown in FIG. 2, the nozzle 8 is configured to be divided into a first ejection opening 9 and a second ejection opening 10. The first ejection opening is located on both side ends across an approximate center of the suction belt 6 and ejects air. The second ejection opening 10 is located on a substantially center portion of the suction belt 6 and ejects air toward the suction belt 6. The arrangement is thus such that the first ejection opening 9 mainly causes the sheets 2 to hover, while the second ejection opening 10 blows air between the suction belt 6 and the uppermost sheet, so that the uppermost sheet is separated from the next sheet, thereby obtaining a sufficient sheet separation effect (e.g., refer to U.S. Pat. No. 5,090,676 and JP-A-2005-1855).